THREE North-East NHS trusts have been identified by the annual Dr Foster Hospital Guide as having significantly higher than expected death rates.

However, the figures from Dr Foster are disputed by the NHS hospitals concerned, which insist that death rates are within the expected range using official Department of Health figures.

According to the independent Dr Foster guide, South Tees Hospitals NHS Foundation Trust, North Tees and Hartlepool NHS Foundation Trust and Northumbria Healthcare NHS Foundation Trust all have significantly higher Hospital Standardised Mortality Ratios, or HSMRs, than expected.

Dr Foster also names the County Durham and Darlington NHS Foundation Trust as one of ten hospital trusts in England to have one or more hospital sites with a mortality rate higher than the overall trust level.

But a joint statement from the North-East NHS trusts named in the Dr Foster guide insisted that all North-East hospitals "remain within the expected range for mortality using the Department of Health's own Summary Hospital-level Mortality Indicator measure" and the public should be reassured that this remains the case.

A spokesman for Dr Foster said: "Expectations are based on various factors that Dr Foster looks at when assessing hospital mortality.

"The most important factors are age, underlying health conditions of patients, and whether their admissions are planned or unplanned.

"Hospitals are then grouped to show where the mortality rate is unlikely to be due to chance."

The North-East NHS spokesman said: "Hospitals across the North-East of England have a very strong track record of providing some of the highest quality of care in the entire NHS and it is important that the public are reassured that this remains the case.

"The mortality indictors being published by Dr Foster should not cause unnecessary alarm and do not directly indicate that any deaths have been caused or contributed to by poor care."

The spokesman said the trusts "are very keen to understand why Dr Foster's own data tells a different story."

NHS bosses revealed that experts are looking in details at hospital mortality in the region.

A spokesman for South Tees Hospitals said the trust board believed that the temporary rise in death rates which occurred during the winter of 2012 was partly due to an increase in the number of elderly patients dying of respiratory illnesses during the unusually long and cold winter.